List of Undervoltage Protection Equipment, Device and Their Function

list of Undervoltage Protection Devices and Their Function

Not only the overvoltage fault can harm the electrical machines, devices, and equipment, but also the Undervoltage fault can affect the electrical machines, devices, and devices very much. When the voltage decreases from its normal level due to any fault, then it is called the Undervoltage fault. So, the protection for the Undervoltage fault is also a very important factor as with overvoltage fault protection. In the previous article, we have discussed the List of Overvoltage Protection Devices and Their Function. In this article, we are going to see the list of Undervoltage Protection Devices and Their Function.

Causes of Undervoltage Fault

Undervoltage fault can occur due to Phase Failure, Loose Contacts, overload in power source, a sudden connection of additional load, Leakage, dead short circuit in the power circuit, etc. so, there are several possible reasons that can decrease the voltage level in a power circuit. The nature of the Undervoltage fault is also a very important factor and here attention is must be required. That means, an Undervoltage fault can happen for an instant or a few seconds, also it may happen for a long time. Sudden and instant Undervoltage causes power fluctuation and it is more harmful than the long-time Undervoltage fault.

Electrical machines, devices, equipment which mostly affected due to Undervoltage Fault

Electric Motors, Electronic Devices such as amplifiers, LED TVs, control systems, automation systems, etc are mostly affected due to the Undervoltage fault. When an Undervoltage fault occurs, the electric motor draws a very high current that damages the coil of the motor and chance of burning or fire. Electronic devices are affected by an Undervoltage fault, their power supply circuit may be damaged, distraction in operation, programs corruption, etc. So, all the sensitive devices can be affected by the Undervoltage fault.

List of Undervoltage Protection Devices

  1. Undervoltage Relay
  2. Stabilizer
  3. Voltage Protector
  4. Monitor Relay
  5. Undervoltage Protection Monitor
  6. Automatic Voltage Regulator (AVR)
  7. Static Transfer Switches (STS)
  8. Voltage Monitoring Relays

Undervoltage Relay

Undervoltage Relays are generally connected to a power system directly(for low-voltage circuits) or through the Potential Transformer or PT(for high-voltage circuits). They are voltage-overrated relays. They are mainly connected to the main incoming power supply circuit breaker through NC or NO contacts. so, in normal conditions, when the voltage is within the limit, the circuit breaker keeps close the circuit, but when the Undervoltage fault occurs, the voltage across the relay also decreased and it sends a signal to the circuit breaker to trip and disconnects the main incoming power supply. Undervoltage Relays are mostly used for the protection of electric motors.

three phase undervoltage relay

Here, you can see the diagram of a three phase undervoltage relay. It has so many terminals, but we have shown only the useful terminal for the undervoltage protection. It has three phases(R,Y,B) and Neutral(N) as inputs. It also has, 'Common', 'NO', and 'NC' contact terminals for the circuit breaker connection.


A stabilizer is a device that is used for the protection of electrical and electronic sensitive equipment from both overvoltage and Undervoltage faults. The stabilizer always provides a constant voltage in its output even the input voltage is extremely high or low. Old electrical stabilizers have a transformer with tapping, according to the voltage it changes it tapping by a motor. Modern stabilizers have electronic circuitry, sensors, and controller which provides a very smooth operation.

Automatic Voltage Regulator (AVR)

An AVR is a device used to regulate and stabilize the output voltage of power sources, such as generators or transformers. It ensures that the voltage remains within acceptable limits even during fluctuations in the input voltage. The AVR continuously monitors the output voltage and compares it to a reference voltage. It maintains a stable output voltage in both Undervoltage and overvoltage faults. In cases of Undervoltage, the AVR increases the voltage to maintain a stable output. We can see the uses of AVR in the Uninterruptible Power Supply(UPS) System.

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List of Undervoltage Protection Equipment, Device and Their Function List of Undervoltage Protection Equipment, Device and Their Function Reviewed by Author on November 03, 2021 Rating: 5
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